This invention relates to compression molding of three-dimensional shaped composite structures, and more particularly it relates to a computer-aided method for laying up of fiber-reinforced resin prepreg materials prior to molding.
Known methods for compression molding of fiber-reinforced composite materials generally include a hand layup of prepreg material in a mold or using a planar sheet of the material and then forming the shape desired by heating and then compressing the sheet in the mold.
In molded shapes requiring high fiber volume and high fiber alignment, the above processes are less than satisfactory because of the inability to precisely control the final fiber location. For example, in the case of resin reinforced with continuous filament fiber materials, the fibers will overlap and wrinkle as they try to conform to complex three-dimensional mold shapes. When the resin is reinforced with discontinuous fibers, such as disclosed in U.S. Pat. No. 4,552,805 the sheet structure will readily draw during the forming process without wrinkling. However, the fiber volume fraction will tend to decrease in areas of high draw in the mold. This results in lower strength and modulus in these high draw areas.
Attempts to compensate for this have been made by hand laying patches of material in those areas of high draw in the mold. The problem of determining the exact location of those areas in the planar sheet and the exact amount of additional material required in those areas has not been addressed in the prior art.